The purpose of this Phase II proposal is to clone and characterize the gene responsible for encoding a bacterial IgM receptor. The resulting recombinant protein will have applications for monitoring IgM antibody responses and have applications for early identification of individuals exposed to pathogen, detection of infection in the newborn and for use in a variety of immunodiagnostic tests to monitor disease progression. In addition, the reagent, when immobilized, can be used to purify IgM antibodies. In the Phase I study we have developed selective assay techniques to screen a large number of isolates for IgM-binding potential which have led to identification of a number of candidate organisms which will he used in the Phase II studies. Using a selected candidate organism, DNA libraries-will be generated and screened to identify the gene encoding the IgM-binding protein. The IgM-binding domain will be identified and a recombinant product suitable for use in immunotechnological applications engineered. The focus of the project is to develop a bacterial IgM receptor for use in a wide variety of diagnostic kits as affinity purification reagents and research reagents for monitoring IgM antibody responses. Commercialization will be the focus of Phase III. PROPOSED COMMERCIAL APPLICATION: A human IgM-binding protein that could bind to the heavy chain without affecting the ability of the antibody to bind antigen would provide a key reagent for research and diagnostic immunoassays. A bacterial protein which could detect IgM in an analogous fashion to Staphylococcal protein A or Streptococcal protein G would also have broad commercial applications for large scale purification of IgM antibodies.